Explain why the simplest can be called the cells of the body?

The protozoan organism consists of one cell, which has in its structure all the necessary inclusions for its life: mitochondria for energy, a nucleus for storing information and protein biosynthesis, as well as ribosomes; Golgi apparatus, vacuoles; cell center, cytoskeleton and other cell organelles. We can say that the simplest is an independent organism, because it does not need someone else’s help for life.
One cell of the body is also an independent unit, which also has everything necessary for life. But the difference between the protozoa and the cell of the body is that the latter work together, together. The cells of the body perform their functions together.
Also, the difference is that the cells of one organism still have differences in their structure and functions. For example, blood cells – red blood cells – do not have the ability to divide. Only nerve cells – neurons – have processes.